At present, the medium which has light modulation effect is mainly classified as four techniques, such as electrochromism, photochromism, thermochromism and piezochromism, wherein the light modulation medium made by photochromism, thermochromism and piezochromism are not completely actively controlled and are significantly influenced by environmental factors.
The well-known light modulation medium invented by Koreans is a suspended particle type light modulating glass made by the electrochromism technique. The glass regulates ray transmission and scattering degrees by controlling the amount of suspended particles between two layers of the light modulating glass. The light modulating glass has the defects of high cost and strict requirements for operation and use conditions in the purpose of preventing particle leakage. Apart from the electrochromism technique, light modulation can also be realized by a mechanical method (referring to PRC utility model patent ZL200320116206.8). The mechanical method is mainly realized by arranging two reels at the two ends of a hollow sandwich glass and wrapping various color films on the reels. When shielding is required, the film of one color is rotated out for shielding. When light transmission is required, the color films are retracted by a motor controlling the reels. So, the work principle is similar to that of a roadside rotating advertisement carrier used in daily life. The difference from the carrier lies in that the thickness can be controlled thinner. The mechanical method has the worst defect that the glass needs to be manually operated and is inconvenient in use.
Besides, a well known light modulation medium, as shown in FIGS. 8 to 10, is an electro-light modulating glass realized by Polymer Dispersed Liquid Crystal (PDLC) technique. The PDLC technique mainly is switched between transmission and scattering in a macroscopic state by controlling the alignment of a liquid crystal after the nematic liquid crystal is mixed with molecular polymers and making the liquid crystal have different refraction indices. Specifically, the technique comprises the following steps: mixing a proper amount of nematic liquid crystal with a certain number of molecular monomers, filling the mixture in the gap between two layers of glass 101 (of a certain thickness) or two layers of plastic substrates 101 to form a mixture layer 103, plating transparent electrodes 102 on the opposite surfaces of the two layers of glass or plastic substrates 101, as shown in FIG. 8, and making the molecular monomers having chemical change and condensed into molecular polymers by carrying out illumination processing with ultraviolet rays of certain wavelength and strength. The polymers are transparent. The liquid crystal molecules are uniformly mixed with the molecular polymers. Therefore, in the process for forming the molecular polymers, the liquid crystal molecules are uniformly cut into small bubble spaces, in other words, the molecular polymers and the liquid crystal molecules are no longer in a mixed state but in a phase separated state, and the molecular polymers bear countless small liquid crystal bubbles. As shown in FIG. 9, with no electric power applied, the alignment of the liquid crystal molecules 201 does not show strong orientation for the different liquid crystal bubbles 220, but is in a relatively random state as a whole. The bonder edge of the liquid crystal bubbles 220 and the molecular polymer carriers 202 has large and irregular change in refraction rates by reason of the anisotropy of the liquid crystal molecules 201 and the refraction rate difference of the large area of molecular polymer carriers 202. Thus, incident rays 210 from one side of the glass or the plastic substrates 101 are scattered in the mixture layer, and the scattered rays 211 are reflected to different directions. The liquid crystal bubbles 220 are small in volume and have large contact area with the molecular polymer carrier 202, so the glass produces obvious scattering phenomena without transmission like a frosted glass. The alignment of the liquid crystal molecules 201 can be controlled to make a change by controlling the electric power applied to the electrodes on the two sides of the glass or plastic substrates 101, as shown in FIG. 10. For example, when AC voltage signals (30V to 200V more or less) of a certain frequency are applied by a power supply 300, the liquid crystal molecules 201 are aligned into an ordered state from a random state. The liquid crystal molecules 201 are aligned in the same direction, and the liquid crystal bubbles 220 are uniformly dispersed in the molecular polymer carriers 202, so when the incident rays 210 pass through the mixture layer, there is a small change in the refraction rate of the rays in the direct incidence direction of the rays. Natural rays 211 are reflected under the condition of weak scattering, producing a certain transparent effect. The electrical light modulating glass applying PDLC technique has strong transparency. However, the PDLC technique is not multi-stable, and the transparent state needs to be maintained by continuously supplying power.